SEASONALITY OF EELGRASS, EPIPHYTE, AND GRAZER BIOMASS AND PRODUCTIVITY IN SUBTIDAL EELGRASS MEADOWS SUBJECTED TO MODERATE TIDAL AMPLITUDE

Epiphyte and eelgrass (Zostera marina L.) biomass and production and h erbivorous gastropod (Lacuna spp.) biomass were measured monthly for t wo years in a subtidal meadow subjected to moderate tidal amplitude in the San Juan Islands, WA, USA. Major physical and chemical factors (e .g., nutrient concentrations, light, and temperature) were measured co ncurrently. Eelgrass biomass varied from 72.2 +/- 16.5 gdw m(-2) in wi nter to 445.0 +/- 78.2 gdw m(-2) (mean +/- 90% CI) in summer. Eelgrass productivity averaged 1767 gdw m(-2) y(-1). Epiphyte biomass varied f rom 2.1 +/- 0.8 gdw m(-2) in winter to 202.3 +/- 99.9 gdw m(-2) in sum mer. Epiphyte production was 577 gC m(-2) in 1990-1991 and 291 gC m(-2 ) during 1991-1992. Light availability was the best predictor of eelgr ass biomass and productivity. With the exception of ammonium, availabi lity of water column nutrients was not positively correlated with meas ures of autotrophic biomass or productivity. Productivity and autotrop hic biomass of this subtidal community are similar to literature maxim a for intertidal meadows.